Generally, the present invention relates to industrial cleaning solvents for removing coatings and adhesives and methods for using these solvents. More specifically, the invention relates to solvents for industrial cleaning and for removing/dissolving urethane, varnish, and epoxy coatings and adhesives.
Urethane materials are commonly used as adhesives, coatings, foam fillers, foam structures, and foam cushions. From an application perspective there is no meaningful-distinction between the terms “urethane” and “polyurethane.” These materials are sometimes formulated as single part compositions and sometimes formulated as multi-part compositions that are mixed prior to application. Sometimes the urethanes are heated (“hot melted”) for applications, sometimes special curing agents such as moisture are used. Urethanes are often applied as coatings to components and are often fabricated as molded mechanical components.
Urethanes are capable of forming strong bonds with other materials such as wood, glass, masonry, and metal. As a consequence urethanes are often used as coatings and adhesives.
Varnish materials were traditionally comprised of a drying oil, a resin, and a solvent. Today, varnishes include a range of natural and synthetic resins including unpigmented and lightly pigmented acrylic, polyurethane, and epoxy. Varnishes can create hard, lustrous, semi-transparent coatings that enhance and protect substrates. Varnishes are often applied to wood products such as furniture, floors, and musical instruments so that the natural aesthetics of the wood are visible yet protected. Varnishes are also widely used in the electrical component industry for sealing and insulating parts such as electric motor windings where they are used as an adhesive sealer. Varnishes are capable of forming strong bonds with other materials such as wood, glass, masonry, and metal. As a consequence, varnishes are often used as coatings and adhesives.
Epoxy materials are commonly used as adhesives, coatings, and as matrix components in the manufacture of composite materials. These materials are copolymers formed from a resin and activator combination creating cross linked arrays of polymer chains. Epoxies are often applied as coatings to components. They are also often used as the bonding matrix in composite materials which are made from other materials with desirable properties such as strength or conductivity. Epoxies are capable of forming strong bonds with other materials such as wood, glass, masonry, and metal. As a consequence, epoxies are often used as coatings and adhesives.
Frequently it is desirable to detach a urethane, varnish, or epoxy from a component, or to separate two components that have been bonded together by a urethane, varnish, or epoxy adhesive. Often it is desirable to detach a coating system comprised of layers of these materials superimposed upon and bonded to each other from a substrate. For many years, dichloromethane (DCM) was the “gold standard” solvent for debonding. However, this solvent has been identified as a hazardous air pollutant, a poison, and a suspected carcinogen. Hence, its use has been eliminated by much of industry and it is highly regulated by government environmental, health, and safety agencies. Halogenated materials like DCM are also unsatisfactory for certain applications in that free halogens which are released by the halogenated hydrocarbons will attack metals such as copper, nickel, and iron. The presence of halogenated stripper residues, which are entrapped on the substrate, can cause latent attack and reliability problems. While a number of replacement solvents have been identified, very few approach the effectiveness of DCM. Also, many of the replacement solvents are flammable, corrosive, highly reactive, or have other characteristics that constitute hazardous wastes under the Resource Conservation and Recovery Act (RCRA) at 42 U.S.C. 6921-6939e. Other replacement materials have various shortcomings such as a pungent odor, the potential for diversion to illicit drug manufacturing, or ineffectiveness in attacking urethanes, varnishes, and epoxies; particularly in thin bond lines.
N-methyl-pyrrolidone (NMP) has been used as a replacement solvent in some applications. The relative strength of N-methyl-pyrrolidone compared to more conventional solvents like DCM is weak. NMP is regulated under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) section 313 and suspected to be a reproductive toxicant. Certain states like California have recognized NMP as a chemical of concern and as a result, some industries have moved away from using this as a solvent. Very few chemicals closely related to NMP (cyclic amides) are liquids at room temperature. Those that are, are less desirable solvents because they are higher in cost and display weaker solvency than NMP. Other solvents that have been used to replace conventional solvents (i.e., benzyl alcohol, dibasic ester, and propylene glycol n-butyl ether) are only modestly effective at removing paints and adhesives. What is needed, therefore, are more effective and practical solvents that can be used in debonding urethane, varnish, and epoxy coatings and adhesives from components.
Solvents designed to remove coatings and adhesives generally consist of up to four types of components: primary solvents, cosolvents, activators, and extenders. Primary solvents are those chosen for their ability to substantially attack the coatings of interest. Cosolvents are chosen to increase the versatility of the solvent with regard to the types of the materials it attacks. Activators are chosen for their catalytic effects; their ability to accelerate penetration of the coating and enable faster, more complete breakdown of the film's molecular bonds. Extenders are chosen to enhance some other desirable characteristic like flash point, drying time, or cost and may also contribute to the overall effectiveness of the solvent.
One such desirable characteristic is lower volatile organic compound (VOC) content. Solvents with lower VOC content have become more desirable as regulations governing VOC emissions have increased. VOC-exempt materials, such as dimethyl carbonate, tertiary butyl acetate, and water, are useful cosolvents and extenders to lower the VOC content of a solvent. The state of California is a leader in regulations that define VOC content limits with regulations that define VOC limits by product type and application. Like California, some states are excluding Low Vapor Pressure (LVP) solvents from the VOC content calculation: The California Air Resource Board (CARB) defines LVPs as solvents that boil above 216° C. or have vapor pressures below 0.1 mm Hg at 20° C.
CARB regulations contain rules that cover solvent VOC limits based on percent by weight, grams/liter, and partial vapor pressure. Increasingly restrictive regulations are creating urgent needs for effective solvents that are safer to use and have lower VOC content. For this reason it is desired to utilize VOC-exempt or LVP cosolvents and extenders when practical.
In addition to these four possible main components of a solvent for removing paint and adhesive, other materials may be used as additives to enhance the solvent's physical characteristics such as thickening agents to increase viscosity, emulsifiers to improve solubility of the solvent's various components, and materials that form floating, evaporative caps, a device particularly useful for reducing evaporation when the solvent is to be used in a heated tank application.